Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0567—Liquid materials characterised by the additives
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/058—Construction or manufacture
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/043—Processes of manufacture in general involving compressing or compaction
  • H01M4/0435—Rolling or calendering
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/0438—Processes of manufacture in general by electrochemical processing
  • H01M4/0459—Electrochemical doping, intercalation, occlusion or alloying
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/049—Manufacturing of an active layer by chemical means
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/134—Electrodes based on metals, Si or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/139—Processes of manufacture
  • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/021—Physical characteristics, e.g. porosity, surface area
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/027—Negative electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/028—Positive electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates to an overlithiated positive electrode, a method of preparing a positive electrode which includes a method of overlithiating the positive electrode, and a lithium secondary battery including the positive electrode.
• an electrochemical device using the electrochemical energy may be a secondary battery and there is a trend that its usage area is expanding more and more.
• demand for secondary batteries as an energy source has been significantly increased as technology development and demand with respect to portable devices, such as portable computers, mobile phones, and cameras, have increased, and, among these secondary batteries, lithium secondary batteries having high energy density, i.e., high capacity have been subjected to considerable research and have been commercialized and widely used.
• a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator.
• the negative electrode includes a negative electrode active material in which lithium ions released from the positive electrode are intercalated and deintercalated, and silicon-containing active material particles having large discharge capacity may be used as the negative electrode active material.
• the silicon-containing active material particle may correspond to silicon (Si) or SiO x (0 ⁇ x ⁇ 2).
• the silicon-containing active material particle has an advantage of large theoretical capacity and low price.
• the silicon-containing active material particle has an excessively large volume change during battery operation, it is disadvantageous in that lifetime of the battery is rapidly decreased as the battery is cycled.
• the silicon-containing active material particle there is a method of using only a portion of total capacity of the silicon-containing active material particles.
• a so-called pre-lithiation process is used in which lithium ions are intercalated into the negative electrode including the silicon-containing active material particles in advance.
• the lithium ions are intercalated into the negative electrode by a method such as transferring lithium metal to the negative electrode, total capacity of the negative electrode may be reduced to a level of reversible capacity as the lithium ions react at irreversible sites of the negative electrode.
• an amount of the lithium ions intercalated during battery operation may be suitably reduced to a level required for the battery operation, the volume change of the silicon-containing active material particles may be minimized.
• An aspect of the present invention provides a method of preparing a positive electrode which does not cause exfoliation or crack generation of an active material when the positive electrode is overlithiated and may significantly shorten time required for an overlithiation process.
• Another aspect of the present invention provides an overlithiated positive electrode in which a decrease in capacity is suppressed, because a cracking phenomenon of the active material during cycle operation is suppressed due to stable overlithiation and formation of a solid electrolyte interface (SEI) film on a surface of the positive electrode, resistance characteristics are excellent, and an amount of lithium decreased is less even during long-term cycles.
• SEI solid electrolyte interface
• Another aspect of the present invention provides a lithium secondary battery in which life characteristics are improved because unique characteristics of a negative electrode active material may be achieved without disadvantages due to the control of an available region of a negative electrode by including the overlithiated positive electrode, a synergistic effect may be expected in improving the life characteristics particularly due to excellent ability to suppress a degradation phenomenon, and a problem of output reduction is minimized even during long-term operation due to a low resistance increase rate.
• a positive electrode including a current collector, and a positive electrode active material layer on the current collector, the positive electrode active material layer comprising a positive electrode active material and a carbonate-containing compound comprising a fluorine-containing functional group.
• XPS X-ray photoelectron spectroscopy
• a method of preparing a positive electrode which includes forming a positive electrode structure comprising a transfer stack comprising a base film and a lithium metal layer on the base film on a preliminary positive electrode active material layer, the lithium metal layer and the preliminary positive electrode active material layer being in contact with each other, and impregnating the positive electrode structure in an electrolyte comprising a carbonate-containing compound comprising a fluorine-containing functional group.
• a lithium secondary battery including the positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode.
• a lithium secondary battery including an electrode assembly comprising an overlithiated positive electrode comprising an overlithiated positive electrode active material layer, a negative electrode comprising silicon particles as an active material, and a separator between the overlithiated positive electrode and the negative electrode, a battery case configured to accommodate the electrode assembly; and an electrolyte injected into the battery case and configured to impregnate the electrode assembly, the electrolyte comprising a carbonate-containing compound comprising a fluorine-containing functional group.
• D 50 in the present specification may be defined as a particle diameter at a cumulative volume of 50% in a particle size distribution curve.
• the D 50 may be measured by using a laser diffraction method.
• the laser diffraction method may generally measure a particle diameter ranging from a submicron level to a few mm and may obtain highly repeatable and high-resolution results.
• a positive electrode which is characterized in that it includes a positive electrode active material layer which includes a positive electrode active material and a carbonate-containing compound containing a fluorine-containing functional group; and a current collector on which the positive electrode active material layer is disposed, wherein, in a C 1s spectrum by X-ray photoelectron spectroscopy (XPS) analysis, a peak intensity I C1 at a binding energy of 288 eV to 292 eV is lower than a peak intensity I C2 at a binding energy of 284 eV to 286 eV.
• XPS X-ray photoelectron spectroscopy
• the positive electrode is an overlithiated positive electrode, wherein, since it is prepared by an overlithiation method to be described later, particularly, by performing a process of impregnation in an electrolyte in which a carbonate-containing compound containing a fluorine-containing functional group is included, the carbonate-containing compound containing the fluorine-containing functional group may be deposited on a surface of the positive electrode and may penetrate into internal pores, and thus, it may suppress a phenomenon of cracking of the positive electrode active material on the surface through a film formed inside and outside the positive electrode from the carbonate-containing compound containing the fluorine-containing functional group which penetrates into the internal pores as well as the surface, and may significantly contribute to suppress degradation of the entire positive electrode during cycle operation.
• the positive electrode according to the embodiment of the present invention is characterized in that pre-lithiation is not performed by typically contacting a lithium metal layer to the negative electrode, but the lithium metal layer is transferred to the positive electrode and rolled and lithium ions intercalated into the positive electrode are then transferred to the negative electrode in a formation process of the battery.
• a phenomenon of exfoliation of the active material which newly occurs in a process of transferring lithium to the positive electrode rather than the negative electrode or a problem of reduction in process efficiency due to long-term overlithiation may be overcome through electrolyte impregnation.
• the negative electrode and the lithium metal layer are not in contact and the lithium ions are not directly intercalated into the negative electrode from the lithium metal layer, a phenomenon of excessive heat generation due to an alloy reaction of lithium and silicon at the negative electrode may be avoided and a possibility of ignition due to a reaction between the lithium and moisture may be significantly reduced. Furthermore, since the lithium ions are not intercalated into the negative electrode during notching and punching the negative electrode (because the pre-lithiation has not progressed), a possibility of ignition during the notching and punching process may be significantly reduced.
• the positive electrode is characterized in that, in a C 1s spectrum by XPS analysis, a peak intensity I C1 of a peak P c1 at a binding energy of 288 eV to 292 eV is lower than a peak intensity I C2 of a peak P c2 at a binding energy of 284 eV to 286 eV.
• the I C2 /the I C1 may preferably be 1 or less, and may be 0.9 or less, 0.8 or less, or 0.7 or less.
• the peak P C1 for example, it appears due to a carbonate-containing by-product, wherein, with respect to the positive electrode according to the embodiment of the present invention, the fluorine-containing carbonate-containing compound is included in the positive electrode active material layer, but since a process of impregnating in the electrolyte is performed, a stable solid electrolyte interface (SEI) film may be formed on the surface and formation of the by-product may be prevented by the formation of the film, and thus, the peak P C1 may appear relatively small.
• SEI solid electrolyte interface
• a peak P C3 at a binding energy of 286 eV to 288 eV may be detected. That is, the peak P C3 may be detected as a weak peak between the peak P C1 and the peak P C2 , and, for example, may appear due to a C-O bond or a C-C-F bond, and it may be a result of the inclusion of the fluorine-containing carbonate-containing compound in the positive electrode active material layer.
• a peak intensity I F1 of a peak P F1 at a binding energy of 687 eV to 689 eV may be lower than a peak intensity I F2 of a peak P F2 at a binding energy of 684 eV to 686 eV.
• the I F2 /the I F1 a ratio of the two peaks, may be 1 or less, and may be 0.8 or less, 0.7 or less, or 0.6 or less.
• peaks may appear due to compounds with functional groups in which fluorine participates in bonding, and, for example, peaks may appear due to compounds having bonds such as C-F, P-F, Li-F, and S-F.
• the peak P F2 is a peak that appears due to a general C-F, P-F, or S-F bond, wherein it may usually be caused by the electrode materials such as the active material and the binder, and may be in a relative relationship with the peak P F2 , for example, in a case in which the peak P F2 appears strong due to a lot of Li-F, the peak P F1 may appear relatively weak.
• a peak intensity I O1 of a peak P O1 at a binding energy of 531 eV to 533 eV may be 4.00 or less, and preferably, may be 3.90 or less, 3.80 or less, or 3.75 or less.
• the bonds usually appeared may not be due to the electrode materials, but may be due to the by-product, and it may mean that the lower the peak intensity I O1 of the peak P O1 is, the smaller the amount of the by-product is.
• the I O1 may be 4.00 or less, and may preferably satisfy the above-described range, and the satisfaction of the range may mean that overlithiation according to an embodiment of the present invention has been performed well such that a stable solid electrolyte interface film has been formed.
• the carbonate-containing compound containing the fluorine-containing functional group may include at least one selected from the group consisting of fluoroethylene carbonate, methyl 2,2,2-trifluoro ethyl carbonate, and 2,2,2-trifluoroethyl carbonate, and may preferably be fluoroethylene carbonate.
• a stable solid electrolyte interface film may be formed on the surface of the positive electrode, and the compound may remain in the positive electrode active material layer.
• the carbonate-containing compound containing the fluorine-containing functional group may be included in an amount of 10 wt% or less based on a total weight of the positive electrode active material layer, and may preferably be included in an amount of 8 wt% or less. This range may be confirmed from the XPS analysis result as described above, wherein some may react with lithium in an overlithiation process, and the remainder may remain in the positive electrode active material layer.
• the positive electrode includes a positive electrode active material layer and a current collector on which the positive electrode active material layer is disposed, wherein the current collector is not particularly limited as long as it has conductivity without causing adverse chemical changes in a battery, and, for example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel that is surface-treated with one of carbon, nickel, titanium, silver, or the like may be used.
• the positive electrode collector may typically have a thickness of 3 ⁇ m to 500 ⁇ m, and microscopic irregularities may be formed on the surface of the collector to improve adhesion of the positive electrode active material.
• the positive electrode collector for example, may be used in various shapes such as that of a film, a sheet, a foil, a net, a porous body, a foam body, a nonwoven fabric body, and the like.
• the positive electrode active material layer may include a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.
• the positive electrode active material is a material capable of causing an electrochemical reaction, wherein it may be a lithium transition metal oxide.
• the positive electrode active material may be composed of the lithium nickel-based oxide, the lithium nickel cobalt manganese composite oxide, the olivine-based lithium metal phosphate, or a combination thereof, and these may be combined to configure the positive electrode active material layer as one layer or a separate layer.
• the positive electrode active material may include a compound of Formula 1 below, and may more specifically be the compound of Formula 1 below.
• the compound of Formula 1 may be in a form of a secondary particle in which a plurality of primary particles are bonded to each other. Specifically, the compound of Formula 1 may be in the form of a secondary particle in which 10 or more primary particles are bonded to each other. Accordingly, there is an effect that lithium may be uniformly intercalated into and deintercalated from the positive electrode active material.
• the positive electrode active material may be included in an amount of 90 wt% to 99 wt%, particularly 92 wt% to 98 wt%, and more particularly 95 wt% to 98 wt% in the positive electrode active material layer.
• the positive electrode active material layer may further include a positive electrode binder.
• the positive electrode binder improves adhesion between the positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode collector.
• Specific examples of the positive electrode binder may be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, an ethylene-propylene-diene polymer (EPDM), a sulfonated-EPDM, a styrene-butadiene rubber (SBR), a fluorine rubber, or various copolymers thereof, and any one thereof or a mixture of two or more thereof may
• PVDF
• the positive electrode binder may be included in an amount of 0.5 wt% to 5.0 wt%, particularly 1.0 wt% to 2.5 wt%, and more particularly 1.0 wt% to 2.0 wt% in the positive electrode active material layer.
• the positive electrode active material layer may further include a positive electrode conductive agent.
• the positive electrode conductive agent is used to provide conductivity to the electrode, wherein any conductive agent may be used without particular limitation as long as it has suitable electron conductivity without causing adverse chemical changes in the battery.
• the positive electrode conductive agent may be graphite such as natural graphite or artificial graphite; carbon based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; powder or fibers of metal such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one thereof or a mixture of two or more thereof may be used.
• graphite such as natural graphite or artificial graphite
• carbon based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers
• powder or fibers of metal such as copper, nickel, aluminum, and silver
• conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers
• conductive metal oxides such as titanium oxide
• conductive polymers such as polyphenylene derivatives
• the positive electrode conductive agent may be included in an amount of 0.5 wt% to 30.0 wt%, particularly 0.5 wt% to 10.0 wt%, and more particularly 1.0 wt% to 4.0 wt% in the positive electrode active material layer.
• a method of preparing a positive electrode according to the present invention is characterized in that it includes steps of: disposing a transfer stack, which includes a base film and a lithium metal layer disposed on the base film, on a preliminary positive electrode active material layer to form a positive electrode structure such that the lithium metal layer and the preliminary positive electrode active material layer are in contact with each other (S1); and impregnating the positive electrode structure in an electrolyte in which a carbonate-containing compound containing a fluorine-containing functional group is included (S2).
• the positive electrode as described above may be prepared by the above preparation method, the prepared positive electrode may have peak characteristics according to the C 1s spectrum, F 1s spectrum, and O 1s spectrum by the XPS analysis, and, since specific details are the same as those described above, descriptions thereof are omitted.
• the method of preparing a positive electrode may further include steps of: rolling the positive electrode structure (S1a); and removing the base film from the transfer stack after the rolling (S1b), between step S1 and step S2.
• step S1, step S1a, step S1b, and step S2 will be sequentially described.
• step S1 of the method of preparing a positive electrode is a step of disposing a transfer stack, which includes a base film and a lithium metal layer, on a preliminary positive electrode active material layer to form a positive electrode structure such that the lithium metal layer and the preliminary positive electrode active material layer are in contact with each other.
• a transfer stack 300 may include a base film 310 and a lithium metal layer 320 disposed on the base film 310.
• the base film 310 may be used without limitation as long as it is a material which may withstand high-temperature conditions that occur in a process of depositing the lithium metal layer 320 on the base film 310.
• the base film may include at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly (methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate.
• a loading amount (unit: mAh/cm 2 ) of the lithium metal layer may be 4% to 40% of a loading amount (unit: mAh/cm 2 ) of the preliminary positive electrode active material layer, and may specifically be 12% to 35%, more specifically, 20% to 30%.
• target lithium intercalation capacity may be easily achieved.
• a preliminary positive electrode active material layer 120' is disposed on a positive electrode collector 110, and the transfer stack 300 may be disposed on the preliminary positive electrode active material layer 120' to form a positive electrode structure 400 such that the lithium metal layer 320 and the preliminary positive electrode active material layer are in contact with each other.
• the preliminary positive electrode active material layer in step S1 may refer to a positive electrode active material layer before overlithiation, and the preliminary positive electrode active material layer may be disposed on the positive electrode collector and may be disposed on one surface or both surfaces of the positive electrode collector.
• the transfer stack 300 may further include a polymer layer 330.
• the polymer layer 330 may be disposed between the base film 310 and the lithium metal layer 320.
• the polymer layer may play a role in effectively peeling off the lithium metal layer from the transfer stack and allowing the lithium metal layer to be easily transferred to the positive electrode active material layer during the preparation of the positive electrode. That is, the polymer layer may be separated from the transfer stack together with the lithium metal layer to be disposed on the positive electrode active material layer.
• the polymer layer may exist in contact with the positive electrode active material layer, and alternatively, the lithium metal layer may exist between the polymer layer and the positive electrode active material layer.
• the polymer layer may be at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly (methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate. Accordingly, in a secondary battery including the positive electrode, since the polymer layer may be dissolved in an electrolyte solution contained in the secondary battery, an increase in resistance of the battery may be prevented. Particularly, the polymer layer may include PMMA, and, in this case, the above-described effect may be further improved.
• the polymer layer may have a thickness of 0.1 ⁇ m to 10 ⁇ m, particularly 0.5 ⁇ m to 5 ⁇ m, and more particularly 1 ⁇ m to 2.5 ⁇ m.
• the lithium metal layer may be easily transferred to the positive electrode active material layer, and a reverse transfer phenomenon, in which the positive electrode active material layer is transferred to the transfer stack, may be prevented.
• step S1a of the method of preparing a positive electrode is a step of rolling the positive electrode structure.
• the pressure applied to the positive electrode structure during the rolling may be in a range of 10 kgf/cm to 90 kgf/cm, particularly, 15 kgf/cm to 80 kgf/cm, and may preferably be 20 kgf/cm or more, 25 kgf/cm or more, or 30 kgf/cm or more, and 70 kgf/cm or less, or 60 kgf/cm or less.
• the lithium metal layer may be effectively transferred, lithium may be intercalated into the positive electrode at a desired level, and the positive electrode active material particles may be controlled such that they are not cracked while not being exfoliated. Accordingly, an effect, which may satisfy both lifetime improvement and capacity characteristics at the same time, may be achieved.
• step S1b of the method of preparing a positive electrode is a step of preparing a positive electrode by removing the base film from the transfer stack after the rolling.
• the method of preparing a positive electrode may further include a step S1b' of resting (leaving alone) the preliminary positive electrode for 1 minute to 600 minutes, specifically, 1 minute to 30 minutes.
• Step S1b' may be performed after step S1a.
• step S1b' may be performed in at least one step of 'between step S1a and step S1b' and 'immediately after step S1b'. Since reaction heat, which has been generated by a reaction of the lithium metal layer and the preliminary positive electrode active material layer in step S1a, may be effectively released by step S1b', lithium is uniformly intercalated into the positive electrode, and thus, there is an effect of reducing the formation of the by-product.
• step S2 is a step of impregnating the prepared positive electrode structure in an electrolyte containing a carbonate-containing solvent.
• lithium since time required for overlithiation may be greatly shortened and a phenomenon of exfoliation or cracking of the active material particles may be suppressed, it may significantly contribute to improve lifetime.
• the present inventors paid attention to the fact that, when overlithiation (pre-lithiation) is performed on the positive electrode, process efficiency is excessively low because the time required for the lithium to be transferred is too long, and the overlithiation of the positive electrode is more difficult in process than the pre-lithiation of the negative electrode due to the active material exfoliation phenomenon that occurs during the transfer, thereby aiming at providing a method of overlithiating the positive electrode using the electrolyte impregnation process.
• the method of preparing a positive electrode according to the embodiment of the present invention may solve problems occurring during the overlithiation of the positive electrode by impregnating the positive electrode structure in the electrolyte, particularly the electrolyte that includes the carbonate-containing compound containing the fluorine-containing functional group.
• a carbonate-containing solvent for example, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, or diethyl carbonate may be used.
• a white layer may be formed on the surface of the positive electrode after the overlithiation, and this may cause an increase in resistance.
• a lithium secondary battery according to an embodiment of the present invention provides a lithium secondary battery including the positive electrode prepared by the above preparation method, a negative electrode, and a separator disposed between the positive electrode and the negative electrode.
• the amount of the lithium in the overlithiated positive electrode active material layer and the amount of the carbonate-containing compound containing the fluorine-containing functional group in the electrode assembly and the electrolyte may be measured by inductively coupled plasma optical emission spectroscopy (ICP-OES).
• ICP-OES inductively coupled plasma optical emission spectroscopy
• a lithium secondary battery which satisfies that the amount of the carbonate-containing compound containing the fluorine-containing functional group in the electrolyte is 3.5 wt% or more based on the total weight of the electrolyte when the amount of the lithium based on the total weight of the positive electrode active material layer in the overlithiated positive electrode is less than 5.0 wt%, may be provided.
• the amount of the lithium is less than 5.0 wt% means that repetitive cycling has progressed for a fairly long period of time, wherein it may mean that degradation of the lithium secondary battery has progressed to some extent.
• the amount of the carbonate-containing compound containing the fluorine-containing functional group in the electrolyte is 3.5 wt% or more based on the total weight of the electrolyte even after the lithium secondary battery has significantly degraded.
• the carbonate-containing compound containing the fluorine-containing functional group may be included as an additive or solvent in the electrolyte, wherein most of them are lost due to a side reaction during cycle operation and, after the degradation has progressed to a significant extent, a residual amount may be considerably small, that is, the amount may be significantly small in a case in which cycles proceed until the amount of the lithium in the positive electrode is decreased to less than 5.0 wt%.
• the positive electrode according to the embodiment of the present invention that is, the overlithiated positive electrode is used
• a loss due to the side reaction on the surface of the positive electrode or an amount consumed for film formation is insignificant, and thus, it may prevent a sudden drop in capacity by remaining in the electrolyte for a long period of time.
• the amount of the carbonate-containing compound containing the fluorine-containing functional group may be 3.5 wt% or more based on the total weight of the electrode assembly and the electrolyte, and may preferably be 4.0 wt% or more, 4.5 wt% or more, 5.0 wt% or more, 5.3 wt% or more, or 5.5 wt% or more. Also, the amount of the carbonate-containing compound containing the fluorine-containing functional group may preferably be 15.0 wt% or less, 10.0 wt% or less, or 9.0 wt% or less.
• the carbonate-containing compound containing the fluorine-containing functional group is generally used in an amount range of about 5 wt% to 40 wt% in the electrolyte, and the 40 wt% may be the maximum amount that may be included. That is, even if the carbonate-containing compound containing the fluorine-containing functional group is included in the maximum amount, it is continuously consumed during cycle operation and the sudden drop in capacity may occur after a certain point when the residual amount almost disappears.
• a lithium secondary battery is characterized in that it includes an electrode assembly that includes an overlithiated positive electrode including an overlithiated positive electrode active material layer, a negative electrode including silicon (Si) particles as an active material, and a separator disposed between the positive electrode and the negative electrode; a battery case accommodating the electrode assembly; and an electrolyte which is injected into the battery case so as to impregnate the electrode assembly and includes a carbonate-containing compound containing a fluorine-containing functional group, wherein, when an amount of the carbonate-containing compound containing the fluorine-containing functional group based on a total weight of the electrode assembly and the electrolyte, which is measured by inductively coupled plasma optical emission spectroscopy (ICP-OES), is 8.0 wt% or less, an amount of lithium based on a total weight of the positive electrode active material layer of the overlithiated positive electrode, which is measured by inductively coupled plasma optical emission spectroscopy (ICP-OES),
• the negative electrode includes a negative electrode active material layer, the negative electrode active material layer may include a negative electrode active material, and a silicon-containing negative electrode active material, a carbon-based negative electrode active material, or a combination thereof may be used as the negative electrode active material.
• the Si is silicon particles, wherein it may be silicon particles (particles formed of silicon), so-called Pure Silicon.
• the silicon particles may effectively improve the capacity of the negative electrode.
• the SiO x (0 ⁇ x ⁇ 2) may be in a form including Si and SiO 2 , and the Si may constitute a phase. That is, x corresponds to a number ratio of oxygen (O) to Si included in the SiO x (0 ⁇ x ⁇ 2).
• the silicon-containing composite particle includes the SiO x (0 ⁇ x ⁇ 2), discharge capacity of the secondary battery may be improved.
• the negative electrode active material may further include a carbon-based negative electrode active material.
• the carbon-based negative electrode active material may include at least one selected from the group consisting of artificial graphite, natural graphite, and graphitized meso-carbon microbeads.
• the negative electrode active material layer may further include a negative electrode binder.
• the negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylate, an ethylene-propylene-diene monomer (EPDM), a sulfonated EPDM, a styrene-butadiene rubber (SBR), a fluorine rubber, poly acrylic acid, and a material having hydrogen thereof substituted with lithium (Li), sodium (Na), or calcium (Ca), or may include various copolymers thereof.
• a porous polymer film for example, a porous polymer film prepared from a polyolefin-based polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or a laminated structure having two or more layers thereof may be used.
• a typical porous nonwoven fabric for example, a nonwoven fabric formed of high melting point glass fibers or polyethylene terephthalate fibers may be used.
• a coated separator including a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and the separator having a single layer or multilayer structure may be optionally used.
• At least one additive for example, a haloalkylene carbonate-containing compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric triamide, a nitrobenzene derivative, sulfur, a quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, an ammonium salt, pyrrole, 2-methoxy ethanol, or aluminum trichloride, may be further included in the electrolyte in addition to the above-described electrolyte components for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving discharge capacity of the battery.
• a haloalkylene carbonate-containing compound such as difluoroethylene carbonate, pyridine, triethylphosphite
• a battery module including the secondary battery as a unit cell and a battery pack including the battery module are provided.
• the battery module and the battery pack may be used as a power source of at least one medium and large sized device selected from a power tool; an electric vehicle (EV); a hybrid electric vehicle; a plug-in hybrid electric vehicle (PHEV); or a power storage system.
• a power tool an electric vehicle (EV); a hybrid electric vehicle; a plug-in hybrid electric vehicle (PHEV); or a power storage system.
• EV electric vehicle
• PHEV plug-in hybrid electric vehicle
• a transfer stack which included a PET film (base film), a polymer layer (2.5 ⁇ m thick) disposed on the PET film and formed of PMMA, and a lithium metal layer (6.0 ⁇ m thick, loading amount of 0.62 mAh/cm 2 ) disposed on the polymer layer and formed of solid-phase lithium metal, was prepared.
• Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 ]O 2 was used as a positive electrode active material.
• the positive electrode active material was in a form of a secondary particle in which a plurality (10 or more) of Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 ]O 2 primary particles were bonded to each other, and an average particle diameter D 50 of the secondary particles was 9 ⁇ m.
• a positive electrode which included a preliminary positive electrode active material layer including the positive electrode active material, PVdF as a positive electrode binder, and carbon nanotubes, as a positive electrode conductive agent, at a weight ratio of 98:1:1 and an aluminum foil (thickness: 6 ⁇ m) as a positive electrode collector, was prepared.
• the preliminary positive electrode active material layer had a loading amount of 4.5 mAh/cm 2 and a thickness of 140 ⁇ m.
• a positive electrode was prepared in the same manner as in Example 1-1 except that the concentration of the electrolyte in which the positive electrode structure was impregnated was 1.0 M.
• the transfer stack was disposed on the preliminary negative electrode active material layer to allow the lithium metal layer to be in contact with the preliminary negative electrode active material layer.
• a positive electrode was prepared in the same manner as in Example 1-5 except that the solvent of the electrolyte in which the positive electrode structure was impregnated was replaced with ethylene carbonate and ethylmethyl carbonate, LiFSI was excluded from the lithium salt, and LiPF 6 was used as the lithium salt.
• the lithium metal layer had a thickness of 6 ⁇ m which was thicker than that in Comparative Example 1-2, wherein a phenomenon was also observed in which a portion of the lithium metal layer was exfoliated from the electrode during an overlithiation reaction.
• Silicon (Si) particles having an average particle diameter D 50 of 5 ⁇ m was used as a negative electrode active material.
• a negative electrode which included a preliminary negative electrode active material layer including the negative electrode active material, carboxymethylcellulose (CMC) as a negative electrode binder, and carbon nanotubes, as a negative electrode conductive agent, at a weight ratio of 80:10:10, was prepared.
• the preliminary negative electrode active material layer had a loading amount of 10 mAh/cm 2 and a thickness of 75 ⁇ m.
• Lithium secondary batteries of Examples 2-2 to 2-6 were prepared in the same manner as in Example 2-1 except that the positive electrodes of Examples 1-2 to 1-6 were respectively used instead of the positive electrode of Example 1-1.
• Example 2-5 since a film formed on the surface by the electrolyte impregnation acted as resistance, it may be confirmed that resistance of Example 2-5 was slightly increased in comparison to those of Comparative Examples 2-1 and 2-4. However, it may be understood that a degree of resistance increase was insignificant compared to the time required for the overlithiation, and, since Example 2-5 using the fluorine-based electrolyte was at an almost equivalent level to that of the case where the electrolyte impregnation was not performed, it may be predicted that there will be no substantial performance degradation due to the resistance increase.

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